Preventing or reducing evaporation from bodies of water is a key aspect of water conservation. Water lost through evaporation cannot be easily replaced, and is not available for use by human beings, for mining, farming or industrial uses. In many cases, water is collected in surface reservoirs and ponds. Many solutions have been put into place to at least partially cover the surface of these bodies of water, thereby limiting evaporation. The solutions have included floating covers, discrete floating modules, and chemical monolayers. Each of these methods has advantages and disadvantages. Floating covers, generally a single sheet of material, are effective at covering a large percentage of the surface, but are difficult to manipulate on large bodies of water. Chemical monolayers are inexpensive, but less effective at reducing evaporation, and can be difficult to separate from the water. Discrete floating elements can be used on large bodies of water, are easy to add and remove, but typically have limited coverage. Commonly used floating elements include hollow plastic spheres, often referred to as “bird balls”. These have limited effectiveness, since the ball shape leaves gaps between adjacent balls. In addition to the prevention of evaporation, coverings may provide a thermal insulation, and also retard the growth of organisms at the water/air interface.
Many designs for these discrete floating elements have been proposed to provide maximum surface coverage, while also addressing the issues of overlap (which wastes material), and the effect of the wind in pushing the individual elements into clumps. Several patents suggest novel, complicated designs, including U.S. Pat. No. 3,938,338 (hexagonal hollow float), U.S. Pat. No. 8,019,208 (round, overlapping discs), U.S. Pat. No. 8,099,804 (hexagonal or octagonal hollow pyramid-shapes). U.S. Pat. No. 8,3442,352 (hexagonal hollow disks that allow water into the lower portion), and U.S. Pat. No. 8,393,486 (aerodynamical hexagonal float)
The discrete floating elements described in the art generally are made with a polyolefin (polypropylene, high density polyethylene shell), and may have a polystyrene or polyurethane foam in the interior for added buoyancy. Polystyrene beads, sheets and other shapes can also be used. UV stabilizers are often used to prevent deterioration from UV light exposure. Carbon black may be added for improved UV resistance, or white pigment (like TiO2) to reduce absorbed solar energy.
In addition to use on bodies of water, floating covering elements also find use as coverings for other liquids, including but not limited to chemical production, anodizing baths, galvanizing baths, plating baths, dyeing baths, sewage treatment, oil waste, and waste ponds containing chemical or toxic substances.
Environmental agencies, such as the US EPA, have been concerned with the noxious odors, and hazards associated with evaporation from many of these chemical and waste ponds.
Problems with the polyolefins, polystyrene, and polyurethanes currently used as fluid coverings is that they have limited chemical resistance, and tend to react and deteriorate when exposed to acids, bases, oxidizers and other strong and highly reactive chemicals. These polymers have relatively poor resistance to UV radiation. Additionally, these polymers are quite flammable.
Fluoropolymers, and polyvinylidene fluoride (PVDF) in particular, are known for their high chemical, weathering, permeation and flammability resistance. Unfortunately, at a density of 1.77 g/cm3, PVDF does not readily float on water or many other fluids. Polyamides also have a high degree of resistance to many chemicals, though not good as for fluoropolymers. At a density of 1.13-1.35 g/cm3, these materials also would fail to float on water, or most other fluids.
Hollow floating polyvinylidene fluoride spheres had been proposed for this application, though the complicated manufacturing process and cost of solid PVDF made the use of these PVDF spheres use as liquid coverings undesirable.
U.S. Pat. No. 8,277,913 and US 2012-0045603 describe self-supporting foamed fluoropolymer structures. Through the use of special foaming techniques, it is possible to produce a foamed fluoropolymer structure having a density below the target density of the fluid needing coverage (i.e. below 1.0 g/cm3 for water). US 2013-0108816 describes foamed fluoropolymer foam-core structures.
It has now been found that floating structures having a fluoropolymer or polyamide outer layer can be used as a covering to solve the problem of evaporation from industrial fluid baths and chemical waste ponds. These structures work over a broad pH range, with most chemical solvents and corrosive chemicals. The structures of the invention provide superior chemical resistance, flame resistance and weathering resistance, and will last much longer than polymers typically used in these applications. The floating structure could be, for example, a foamed fluoropolymer, a foamed polyamide, a hollow fluoropolymer or polyamide structure—preferably a foamed hollow structure, or a multi-layer structure having a fluoropolymer or polyamide layer as the outermost layer—such as a polyamide or fluoropolymer coated thermoplastic.
In addition to reducing the evaporation from bodies of fluids, the floating structures of the invention also aid in the thermal insulation (to prevent the fluid body from cooling or warming), prevents splashing when an object is placed into a bath, and prevents misting from a chemical reaction within the bath that releases bubbles. The use of foamed structures reduces costs, as less material is required, and increases the flexibility of the structures.